JavaScript
Numbers
JavaScript
has only one type of number.
Numbers can
be written with, or without, decimals.
JavaScript
Numbers
JavaScript
numbers can be written with, or without decimals:
Example
var
x = 34.00; // A number with decimals
var
y = 34; // A number without
decimals
Extra large
or extra small numbers can be written with scientific (exponent) notation:
Example
var
x = 123e5; // 12300000
var
y = 123e-5; // 0.00123
JavaScript
Numbers are Always 64-bit Floating Point
Unlike many
other programming languages, JavaScript does not define different types of
numbers, like integers, short, long, floating-point etc.
JavaScript
numbers are always stored as double precision floating point numbers, following
the international IEEE 754 standard.
This format
stores numbers in 64 bits, where the number (the fraction) is stored in bits 0
to 51, the exponent in bits 52 to 62, and the sign in bit 63:
Value (aka
Fraction/Mantissa) Exponent Sign
52 bits (0 -
51) 11 bits (52 - 62) 1 bit (63)
Precision
Integers
(numbers without a period or exponent notation) are considered accurate up to
15 digits.
Example
var
x = 999999999999999; // x will be
999999999999999
var
y = 9999999999999999; // y will be
10000000000000000
»
The maximum
number of decimals is 17, but floating point arithmetic is not always 100%
accurate:
Example
var
x = 0.2 + 0.1; // x will be
0.30000000000000004
Try it
yourself »
To solve the
problem above, it helps to multiply and divide:
Example
var
x = (0.2 * 10 + 0.1 * 10) / 10; //
x will be 0.3
»
Hexadecimal
JavaScript
interprets numeric constants as hexadecimal if they are preceded by 0x.
Example
var
x = 0xFF; // x will be 255
»
Never write
a number with a leading zero (like 07).
Some
JavaScript versions interpret numbers as octal if they are written with a
leading zero.
By default,
JavaScript displays numbers as base 10 decimals.
But you can
use the toString() method to output numbers as base 16 (hex), base 8 (octal),
or base 2 (binary).
Example
var
myNumber = 128;
myNumber.toString(16); // returns 80
myNumber.toString(8); // returns 200
myNumber.toString(2); // returns 10000000
»
Infinity
Infinity (or
-Infinity) is the value JavaScript will return if you calculate a number outside
the largest possible number.
Example
var
myNumber = 2;
while
(myNumber != Infinity) { //
Execute until Infinity
myNumber = myNumber * myNumber;
}
Division by
0 (zero) also generates Infinity:
Example
var
x = 2 / 0; // x will be Infinity
var
y = -2 / 0; // y will be
-Infinity
»
Infinity is
a number: typeof Infinity returns number.
Example
typeof
Infinity; // returns
"number"
»
NaN - Not a
Number
NaN is a
JavaScript reserved word indicating that a number is not a legal number.
Trying to do
arithmetic with a non-numeric string will result in NaN (Not a Number):
Example
var
x = 100 / "Apple"; // x will
be NaN (Not a Number)
»
However, if
the string contains a numeric value , the result will be a number:
Example
var
x = 100 / "10"; // x will
be 10
»
You can use
the global JavaScript function isNaN() to find out if a value is a number.
Example
var
x = 100 / "Apple";
isNaN(x); // returns true because x is Not
a Number
»
Watch out
for NaN. If you use NaN in a mathematical operation, the result will also be
NaN:
Example
var
x = NaN;
var
y = 5;
var
z = x + y; // z will be NaN
»
Or the result might be a concatenation:
Example
var
x = NaN;
var
y = "5";
var
z = x + y; // z will be NaN5
»
NaN is a
number, and typeof NaN returns number:
Example
typeof
NaN; // returns
"number"
»
Numbers
Can be Objects
Normally
JavaScript numbers are primitive values created from literals: var x = 123
But numbers
can also be defined as objects with the keyword new: var y = new Number(123)
Example
var
x = 123;
var
y = new Number(123);
// typeof x
returns number
// typeof y
returns object
Try it
yourself »
Do not
create Number objects. It slows down execution speed.
The new
keyword complicates the code. This can produce some unexpected results:
When using
the == operator, equal numbers are equal:
Example
var
x = 500;
var
y = new Number(500);
// (x == y)
is true because x and y have equal values
»
When using
the === operator, equal numbers are not equal, because the === operator expects
equality in both type and value.
Example
var
x = 500;
var
y = new Number(500);
// (x === y)
is false because x and y have different types
»
Or even
worse. Objects cannot be compared:
Example
var
x = new Number(500);
var
y = new Number(500);
// (x == y)
is false because objects cannot be compared
»
Note the
difference between (x==y) and (x===y).
Comparing
two JavaScript objects will always return false.
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